For efficiency, H.265 is one of the better codecs to use for the same bitrate as H.264, MPEG-2, or other older codecs. However, H.265 only really shines in higher resolutions. For lower resolution content, H.264 is still fine. The other thing of note is the audio that the ripped content comes with. That can take a significant amount of space if you want 5.1 surround and all that.
I use Handbrake to convert my ripped videos. In the best case I've been able to crunch a ~20GB Blu-Ray rip to about 8GB. But sometimes I get 14-15GB conversions and I've yet to figure out what's causing that. DVD rips tend to go down to about 1GB from 4GB.